To explore the effects of toosendanin in inducing apoptosis of human hepatocarcinoma cell line SMMC-7721 and Hep3B, and its influence on the related genes, Bcl-2, Bax and Fas.The inhibitory rate of cell proliferation and cell growth curve were detected by MTT assay; morphological changes of cells were observed by inverted microscope; early stage apoptosis rate were detected by Annexin V-FITC/PI assay; relative activities of Caspase-3,-8 and-9 were analyzed by spectrophotometry; and the expressions of Bcl-2, Bax and Fas were detected using immunohistochemistry assay.Toosendanin presented significant inhibitory effect on proliferation of hepatocarcinoma cells in a time- and dose-dependent manner. After toosendanin treatment, the amount of cells was significantly reduced, shrunk in size and rounded in shape, with decreased adhesion ability. The apoptosis rates of SMMC-7721 cells and Hep3B cells treated with 0.5 micromol/L toosendanin for 72 h were 21.55% and 18.35% respectively, which were reduced after z-VAD-fmk (inhibitor of Caspase) treatment. The activities of Caspase-3,-8 and -9 all markedly enhanced after treatment in SMMC-7721 cells, while in Hep3B cells, activities of Caspase-3 and -9 enhanced, but that of Caspase-8 unchanged. As compared with the control group, after toosendanin treatment, expression of Bcl-2 decreased, and that of Bax and Fas increased in SMMC-7721 cells; but in Hep3B cells the expression of Bcl-2 decreased, that of Bax increased, and expression of Fas unchanged.Toosendanin could inhibit the proliferation and induce the apoptosis of both P53 and P53 human hepatocarcinoma cells, which involved the participation of mitochondria-dependent pathway. So it may be a kind of natural anti-cancer drug, playing its effect through P53 independent pathway.